Interferometric Synthetic Aperture Radar (ISAR) is a pulse radar system that enables the ability for wide area mapping at high resolutions for numerous applications, including military systems, earth-mapping, and environmental resource mapping. This mapping typically requires transmission of a radio frequency (RF) pulse from a single antenna, and reception of the reflected pulse into two or more antennas at a known antenna-to-antenna spacing. The phase difference of the received pulse in each of the receiving antennas is used to determine a cross-track vector. The accuracy of the ISAR system is directly related to this cross-track vector.
Components in an electronic RF system such as ISAR have an electrical phase dependency on temperature. Uncalibrated differences between receive channels results in electrical phase error over temperature, therefore decreasing ISAR accuracy. Thus, accurate phase calibration over temperature is required for proper system performance.
It is conceptually possible to phase calibrate an ISAR system over temperature by injecting a planar wavefront (to simulate a distant reflected target) into the antennas and measuring the phase differences. Such a calibration, however, would need to take place in a relatively large RF anechoic chamber, which is designed to suppress reflected RF signals. Implementing the extreme temperature variations required for calibration would not be feasible, since phase calibration in an anechoic chamber is feasible only at room temperature and nominal environmental conditions.